Re: [Qemu-devel] is there a limit on the number of in-flight I/O operations?

[Benoît Canet]

The Saturday 19 Jul 2014 à 09:23:50 (+0200), Paolo Bonzini wrote :
> Il 19/07/2014 08:27, Chris Friesen ha scritto:
> > Does it track in-flight operations though?  Or just how many operations
> > can be requested in a given amount of time?
> 
> It should track in flight operations.  However, I'm not sure it supports
> the iops=0 case properly, since I do not see anything in
> tracked_request_end that ceases the accounting of the current operation.
>  Benoit, can you answer?
> 
> Paolo

I think in the throttling case the number of in flight operation is limited by
the emulated hardware queue. Else request would pile up and throttling would be
inefective.

So this number should be around: #define VIRTIO_PCI_QUEUE_MAX 64 or something 
like than that.

> 
> > If it tracks how many operations can be requested, then if the "iops"
> > parameter is larger than what the server can maintain then the number of
> > in-flight operations could still grow indefinitely.
> > 
> > I suppose I'll have to check the code. :)
>